Golf ball having a hollow center

ABSTRACT

A golf ball includes a thermoset spherical inner core shell layer having an outer surface, an inner surface, and an inner diameter to define a hollow center; a thermoset outer core layer formed about the shell layer; and an inner and outer cover layer formed about the outer core layer. The inner cover includes an ionomeric material and the outer cover layer includes a polyurea or a polyurethane having a hardness less than the inner cover layer. The hollow center has a diameter of about 0.51 to 1.1 inches, the shell layer has a surface hardness greater than an inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient, and the outer core layer has a second hardness gradient different from the first.

FIELD OF THE INVENTION

This invention relates generally to golf balls with a core having a hollow center surrounded by one or more core layers and one or more cover layers. Any of the core or cover layers may have a ‘negative’ or ‘positive’ hardness gradient, depending on the desired construction. More particularly, the golf ball includes a core having a hollow center surrounded by a thermoset ‘shell layer’ and at least one additional core layer that is thermoset.

BACKGROUND OF THE INVENTION

In recent years, virtually all golf balls are of a solid construction, typically including with a solid core encased by a cover, both of which can have multiple layers, such as a dual core having a solid center and an outer core layer, or a multi-layer cover having an inner and outer cover layer. Golf ball cores and/or centers are formed from a thermoset rubber composition with polybutadiene as the base rubber. The cores are usually heated and crosslinked to create a core having certain pre-determined characteristics, such as compression or hardness, which result in a golf ball having the properties for a particular group of players, whether it be professionals, low-handicap players, or mid-to-high handicap golfers. From the perspective of a golf ball manufacturer, it is desirable to have cores exhibiting a wide range of properties, such as resilience, durability, spin, and “feel,” because this enables the manufacturer to make and sell golf balls suited to differing levels of ability.

There remains a need, however, for golf ball constructions that allow differing properties to be achieved. One such novel construction with no past commercial success is a golf ball having a hollow core—meaning the innermost portion of the core is hollow surrounded by a ‘shell layer’ and one or more core and cover layers. While, in the past, many commercially-available golf balls have been constructed with non-solid centers, such as liquid centers, very few golf balls having hollow centers have ever been constructed.

While the patent literature references, mostly in a cursory manner, a hollow core as a suitable general alternative construction, very few are actually directed to a hollow core golf ball. For example, U.S. Pat. No. 6,315,683 is generally directed to an over-sized (greater than 1.70 inches) hollow solid golf ball where the hollow core is contained in a thermoset rubber layer and covered with a single ionomer cover. More recently, U.S. Pat. No. 8,262,508 generally describes a golf ball having a hollow center, a mid-layer, an inner cover, and an outer cover. The hollow center and mid-layer are both formed from a thermoset rubber composition, and a conventional ‘positive hardness gradient’ (layer hardness gets softer in the direction of the interior of the layer). The hollow ‘space’ has a diameter of 0.08 to 0.5 inches and the core layer has a low surface hardness of 25 to 55 Shore C. The golf ball is covered by a harder ionomer outer cover and a softer ionomer inner cover.

The inventive golf ball, however, has a hollow core surrounded by a thermoset ‘shell layer’, a thermoset outer cover layer, optionally, one or more thermoset or thermoplastic intermediate core layers, and one or more cover layers. Combining the hollow core construction with variations in the hardness gradients of the adjoining thermoplastic and/or thermoset core layers solves many of the problems associated with previous attempts at hollow core constructions.

SUMMARY OF THE INVENTION

The present invention is directed to a golf ball including a hollow core. The golf ball includes a spherical inner core shell layer formed from a first thermoset rubber composition. The shell layer has an outer surface, an inner surface, and an inner diameter to define the hollow center. An outer core layer is formed around the shell layer and includes a thermoset material, in one embodiment different from the thermoset material used to form the shell layer. An inner cover layer may be formed about the outer core layer and in a preferred embodiment includes an ionomeric material. An outer cover layer is typically formed about the optional inner cover layer or directly over the core. The outer cover is formed from a polyurea or a polyurethane material and preferably has a second hardness less than that of the inner cover layer, if present.

The hollow center has a diameter of about 0.51 to 1.1 inches. The thermoset shell layer has a surface hardness greater than its inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient. The outer core layer has a second hardness gradient different from the first.

Preferably, the shell layer has a surface hardness greater than about 55 Shore C. In one embodiment, the spherical inner core shell layer has a coefficient of restitution (COR) less than about 0.700 when measured at an incoming velocity of 125 ft/s. Alternatively, the outer core layer has a coefficient of restitution, measured at an incoming velocity of 125 ft/s, higher than the coefficient of restitution, measured at an incoming velocity of 125 ft/s, of the inner core shell layer by 10-50%.

In one embodiment, the second hardness gradient is about 0 Shore C. In an additional embodiment, the second hardness gradient is a negative hardness gradient of about 2 to 25 Shore C. In still another preferred embodiment, the second hardness gradient is a positive hardness gradient of about 3 to 10 Shore C. The inner cover may have a hardness greater than about 60 Shore D and the outer cover layer may have a hardness of less than about 60 Shore D. The golf ball typically has a first volume and the hollow center typically has a second volume that is about 2% to 30% of the first volume.

The invention is also directed to a golf ball comprising a hollow core, the golf ball including a spherical inner core shell layer formed from a first thermoset rubber composition, the shell layer having an outer surface, an inner surface, and an inner diameter to define a hollow center. In this preferred embodiment, an outer core layer is formed from a second thermoset material and a thermoplastic intermediate core layer is disposed between the shell layer and the outer core layer. An optional inner cover layer is formed about the outer core layer. The optional inner cover may include an ionomeric material and having a material hardness greater than about 60 Shore D. The golf ball also includes an outer cover layer, which typically is formed from a polyurea or a polyurethane material and has a material hardness of less than about 60 Shore D.

The hollow center has a diameter of about 0.15 to 1.1 inches, the shell layer has a surface hardness greater than an inner surface hardness by about 10 to 25 Shore C to define a first hardness gradient, and the thermoset outer core layer has a second hardness gradient different from the first.

In one embodiment, the second hardness gradient is about 0 Shore C. In an alternative embodiment, the second hardness gradient is a negative hardness gradient of about 2 to 25 Shore C. In still another embodiment, the second hardness gradient is a positive hardness gradient of about 3 to 10 Shore C. In a preferred alternative embodiment, a thermoset intermediate core layer is disposed between the shell layer and the outer core layer, the intermediate core layer comprising a third thermoset rubber composition which may be the same or different than that of the shell or outer core layers.

DETAILED DESCRIPTION OF THE INVENTION

The golf balls of the present invention may include multi-layer golf balls, such as one having a core and a cover surrounding the core, but are preferably formed from a core having a hollow core and at least one outer core layer, an inner cover layer, and an outer cover layer. Any of the core or cover layers may include more than one layer. The cover layer of the golf ball may be a single layer or formed of a plurality of layers, such as an inner cover layer and an outer cover layer.

The hollow core is formed of a thermoset ‘shell layer’ that contains a spherical hollow portion in its interior. In a preferred embodiment, the golf ball includes the thermoset hollow core and at least two outer core layers, where the shell layer is formed from a thermoset material, an outer core layer is formed from a thermoset material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoplastic material. In an alternative preferred embodiment, the golf ball includes the thermoset hollow core and at least two outer core layers, where the shell layer is formed from a thermoset material, an outer core layer is formed from a thermoset material, and an intermediate core layer, disposed between the shell layer and the outer core layer, is formed from a thermoset material.

The shell, outer core, or intermediate core layers may have either a conventional “hard-to-soft” hardness gradient (i.e., the outermost surface/portion of the layer is harder than the innermost surface/portion), known as a “positive hardness gradient,” or a “soft-to-hard” hardness gradient (i.e., a “negative” hardness gradient) as measured radially-inward from the outer surface or portion of each component towards the innermost portion (i.e., from the outer surface/portion towards the inner surface/portion of the shell and/or core layers). As used herein, the terms “negative” and “positive,” with respect to hardness gradient, refer to the result of subtracting the hardness value at the innermost portion of the component being measured (e.g., the inner surface of a core layer) from the hardness value at the outer surface of the component being measured (e.g., the outer surface of an outer core layer). For example, if the outer surface of a core layer has a lower hardness value than at the inner surface, the hardness gradient will be deemed a “negative” gradient (a smaller number−a larger number=a negative number), although the magnitude may be disclosed in the application as the absolute value of the subtraction result in combination with the designation ‘negative’).

The thermoplastic shell, intermediate core layers, and outer core layers of the invention may have ‘positive hardness gradients’ or ‘negative hardness gradients’, as described above. Alternatively, the TP layers may have a ‘zero hardness gradient’, defined herein to include a 0 Shore C hardness gradient ±2 Shore C. The TP layer ‘positive hardness gradient’ or ‘negative hardness gradient’ may be from about 0 Shore C to about 10 Shore C, more preferably about 2 Shore C to about 8 Shore C, and most preferably about 3 Shore C to about 5 Shore C.

The thermoset shell, intermediate core layers, and outer core layers of the invention may have ‘positive hardness gradients’ or ‘negative hardness gradients’, as described above. Alternatively, the TS layers may have a ‘zero hardness gradient’, defined herein to include a 0 Shore C hardness gradient ±2 Shore C. The TS layer ‘positive hardness gradient’ or ‘negative hardness gradient’ may be from about 1 Shore C to about 30 Shore C, preferably about 2 Shore C to about 27 Shore C, more preferably about 5 Shore C to about 25 Shore C, and most preferably about 10 to 20 Shore C. Other suitable TS ‘positive hardness gradient’ or ‘negative hardness gradient’ core layers can be found in U.S. Pat. Nos. 7,537,529 and 7,537,530, the disclosures of which are incorporated herein, in their entirety, by reference thereto.

A variety of the above TS and TP hardness gradient layers are envisioned and both ‘positive hardness gradients’ and/or ‘negative hardness gradients’ may be combined to form the hollow cores of the invention having various layers of this nature.

The surface hardness of the shell or core layers is obtained from the average of a number of measurements taken from opposing hemispheres of the particular layer, taking care to avoid making measurements on the parting line or any surface defects, such as holes or protrusions. Hardness measurements are made pursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic by Means of a Durometer.” Because of the curved surface of the hollow core or core layers, care must be taken to insure that they are centered under the durometer indentor before a surface hardness reading is obtained. A calibrated, digital durometer, capable of reading to 0.1 hardness units is used for all hardness measurements and is set to take hardness readings 1 second after the maximum reading is obtained. The digital durometer must be attached to, and its foot made parallel to, the base of an automatic stand, such that the weight on the durometer and attack rate conform to ASTM D-2240.

To prepare the hollow core for hardness and hardness gradient measurements, the core (shell layer or with one or two core layers) is gently pressed into a hemispherical holder having an internal diameter approximately slightly smaller than the diameter of the core, such that the core is held in place in the hemispherical portion of the holder while concurrently leaving the geometric central plane of the core exposed. The core is secured in the holder by friction, such that it will not move during the cutting and grinding steps, but the friction is not so excessive that distortion of the natural shape of the core would result. The core is secured such that the parting line of the core is roughly parallel to the top of the holder. The diameter of the core is measured 90° to this orientation prior to securing. A measurement is also made from the bottom of the holder to the top of the core to provide a reference point for future calculations. A rough cut, made slightly above the exposed geometric center of the core using a band saw or other appropriate cutting tool, making sure that the core does not move in the holder during this step. The remainder of the core, still in the holder, is secured to the base plate of a surface grinding machine. The exposed ‘rough’ core surface is ground to a smooth, flat surface, revealing the hollow center of the core, which can be verified by measuring the height of the bottom of the holder to the exposed surface of the core, making sure that exactly half of the original height of the core, as measured above, has been removed to within ±0.004 inches.

Leaving the core in the holder, the center of the core is found with a center square and carefully marked and the hardness is measured at the center mark. Hardness measurements at any distance from the center of the core may be measured by drawing a line radially outward from the center mark, and measuring and marking the distance from the center, typically in 1- or 2-mm increments. All hardness measurements performed on the plane passing through the hollow center are performed while the core is still in the holder and without having disturbed its orientation, such that the test surface is constantly parallel to the bottom of the holder. The hardness difference from any predetermined location on the core is calculated as the average surface hardness minus the hardness at the appropriate reference point.

One or more of the shell layer and/or core layers may be formed from a composition including at least one thermoset base rubber, such as a polybutadiene rubber, cured with at least one peroxide and at least one reactive co-agent, which can be a metal salt of an unsaturated carboxylic acid, such as acrylic acid or methacrylic acid, a non-metallic coagent, or mixtures thereof. Preferably, a suitable antioxidant is included in the composition. An optional ‘soft and fast agent’ (sometimes called a cis-to-trans catalyst), such as an organosulfur or metal-containing organosulfur or thiol compound, can also be included in the core formulation. Other ingredients that are known to those skilled in the art may be used, and are understood to include, but not be limited to, density-adjusting fillers, process aides, plasticizers, blowing or foaming agents, sulfur accelerators, and/or non-peroxide radical sources.

The base thermoset rubber, which can be blended with other rubbers and polymers, typically includes a natural or synthetic rubber. A preferred base rubber is 1,4-polybutadiene having a cis structure of at least 40%, preferably greater than 80%, and more preferably greater than 90%.

Examples of desirable polybutadiene rubbers include BUNA® CB22 and BUNA® CB23, CB1221, CB1220, CB24, and CB21, commercially-available from LANXESS Corporation; UBEPOL® 360L and UBEPOL® 150L and UBEPOL-BR rubbers, commercially available from UBE Industries, Ltd. of Tokyo, Japan; KINEX® 7245, KINEX® 7265, and BUDENE 1207 and 1208, commercially available from Goodyear of Akron, Ohio; SE BR-1220; Europrene® NEOCIS® BR 40 and BR 60, commercially available from Polimeri Europa; and BR 01, BR 730, BR 735, BR 11, and BR 51, commercially available from Japan Synthetic Rubber Co., Ltd; PETROFLEX® BRNd-40; and KARBOCHEM® ND40, ND45, and ND60, commercially available from Karbochem.

From the Lanxess Corporation, most preferred are the Nd- and Co-catalyzed grades, but all of the following may be used: BUNA CB 21; BUNA CB 22; BUNA CB 23; BUNA CB 24; BUNA CB 25; BUNA CB 29 MES; BUNA CB Nd 40; BUNA CB Nd 40 H; BUNA CB Nd 60; BUNA CB 55 NF; BUNA CB 60; BUNA CB 45 B; BUNA CB 55 B; BUNA CB 55 H; BUNA CB 55 L; BUNA CB 70 B; BUNA CB 1220; BUNA CB 1221; BUNA CB 1203; BUNA CB 45. Additionally, numerous suitable rubbers are available from JSR (Japan Synthetic Rubber), UBEPOL sold by Ube Industries Inc, Japan, BST sold by BST Elastomers, Thailand; IPCL sold by Indian Petrochemicals Ltd, India; NITSU sold by Karbochem or Karbochem Ltd of South Africa; PETROFLEX of Brazil; LG of Korea; and Kuhmo Petrochemical of Korea.

The base rubber may also comprise high or medium Mooney viscosity rubber, or blends thereof. A “Mooney” unit is a unit used to measure the plasticity of raw or unvulcanized rubber and is defined according to ASTM D-1646. The Mooney viscosity range is preferably greater than about 40, more preferably in the range from about 40 to 60 and most preferably in the range from about 40 to 52.

Commercial sources of suitable polybutadienes include Bayer AG CB23 (Nd-catalyzed), which has a Mooney viscosity of around 50 and is a highly linear polybutadiene, and CB1221 (Co-catalyzed). If desired, the polybutadiene can also be mixed with other elastomers known in the art, such as other polybutadiene rubbers, natural rubber, styrene butadiene rubber, and/or isoprene rubber in order to further modify the properties of the core. When a mixture of elastomers is used, the amounts of other constituents in the core composition are typically based on 100 parts by weight of the total elastomer mixture.

In one preferred embodiment, the base rubber comprises a Nd-catalyzed polybutadiene, a rare earth-catalyzed polybutadiene rubber, or blends thereof. If desired, the polybutadiene can also be mixed with other elastomers known in the art such as natural rubber, polyisoprene rubber and/or styrene-butadiene rubber in order to modify the properties of the core. Other suitable base rubbers include thermosetting materials such as, ethylene propylene diene monomer rubber, ethylene propylene rubber, butyl rubber, halobutyl rubber, hydrogenated nitrile butadiene rubber, nitrile rubber, and silicone rubber.

Suitable peroxide initiating agents include dicumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy) hexane; 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne; 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; 2,2′-bis(t-butylperoxy)-di-iso-propylbenzene; 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane; n-butyl 4,4-bis(t-butyl-peroxy)valerate; t-butyl perbenzoate; benzoyl peroxide; n-butyl 4,4′-bis(butylperoxy) valerate; di-t-butyl peroxide; or 2,5-di-(t-butylperoxy)-2,5-dimethyl hexane, lauryl peroxide, t-butyl hydroperoxide, α-α bis(t-butylperoxy)diisopropylbenzene, di(2-t-butyl-peroxyisopropyl)benzene, di-t-amyl peroxide, di-t-butyl peroxide. Preferably, the rubber composition includes from about 0.25 to about 5.0 parts by weight peroxide per 100 parts by weight rubber (phr), more preferably 0.5 phr to 3 phr, most preferably 0.5 phr to 1.5 phr. In a most preferred embodiment, the peroxide is present in an amount of about 0.8 phr. These ranges of peroxide are given assuming the peroxide is 100% active, without accounting for any carrier that might be present. Because many commercially available peroxides are sold along with a carrier compound, the actual amount of active peroxide present must be calculated. Commercially-available peroxide initiating agents include DICUP™ family of dicumyl peroxides (including DICUP™ R, DICUP™ 40C and DICUP™ 40KE) available from Crompton (Geo Specialty Chemicals). Similar initiating agents are available from AkroChem, Lanxess, Flexsys/Harwick and R.T. Vanderbilt. Another commercially-available and preferred initiating agent is TRIGONOX™ 265-50B from Akzo Nobel, which is a mixture of 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane and di(2-t-butylperoxyisopropyl)benzene. TRIGONOX™ peroxides are generally sold on a carrier compound.

Suitable reactive co-agents include, but are not limited to, metal salts of diacrylates, dimethacrylates, and monomethacrylates suitable for use in this invention include those wherein the metal is zinc, magnesium, calcium, barium, tin, aluminum, lithium, sodium, potassium, iron, zirconium, and bismuth. Zinc diacrylate (ZDA) is preferred, but the present invention is not limited thereto. ZDA provides golf balls with a high initial velocity. The ZDA can be of various grades of purity. For the purposes of this invention, the lower the quantity of zinc stearate present in the ZDA the higher the ZDA purity. ZDA containing less than about 10% zinc stearate is preferable. More preferable is ZDA containing about 4-8% zinc stearate. Suitable, commercially available zinc diacrylates include those from Sartomer Co. The preferred concentrations of ZDA that can be used are about 10 phr to about 40 phr, more preferably 20 phr to about 35 phr, most preferably 25 phr to about 35 phr. In a particularly preferred embodiment, the reactive co-agent is present in an amount of about 29 phr to about 31 phr.

Additional preferred co-agents that may be used alone or in combination with those mentioned above include, but are not limited to, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, and the like. It is understood by those skilled in the art, that in the case where these co-agents may be liquids at room temperature, it may be advantageous to disperse these compounds on a suitable carrier to promote ease of incorporation in the rubber mixture.

Antioxidants are compounds that inhibit or prevent the oxidative breakdown of elastomers, and/or inhibit or prevent reactions that are promoted by oxygen radicals. Some exemplary antioxidants that may be used in the present invention include, but are not limited to, quinoline type antioxidants, amine type antioxidants, and phenolic type antioxidants. A preferred antioxidant is 2,2′-methylene-bis-(4-methyl-6-t-butylphenol) available as VANOX® MBPC from R.T. Vanderbilt. Other polyphenolic antioxidants include VANOX® T, VANOX® L, VANOX® SKT, VANOX® SWP, VANOX® 13 and VANOX® 1290.

Suitable antioxidants include, but are not limited to, alkylene-bis-alkyl substituted cresols; substituted phenols; alkylene bisphenols; and alkylene trisphenols. The antioxidant is typically present in an amount of about 0.1 phr to 5 phr, preferably from about 0.1 phr to 2 phr, more preferably about 0.1 phr to 1 phr. In an alternative embodiment, the antioxidant should be present in an amount to ensure that the hardness gradient of the core layers is “negative.” Preferably, about 0.2 phr to 1 phr antioxidant is added to the core layer formulation, more preferably, about 0.3 to 0.8 phr, and most preferably 0.4 to 0.7 phr. Preferably, about 0.25 phr to 1.5 phr of peroxide as calculated at 100% active can be added to the core formulation, more preferably about 0.5 phr to 1.2 phr, and most preferably about 0.7 phr to 1.0 phr. The ZDA amount can be varied to suit the desired compression, spin and feel of the resulting golf ball. The cure regime can have a temperature range from about 290° F. to 350° F., more preferably about 300° F. to 335° F., and the stock is held at that temperature for about 10 minutes to 30 minutes.

The thermoset rubber compositions may also include an optional ‘soft and fast agent’. As used herein, “soft and fast agent” means any compound or a blend thereof that that is capable of making a core 1) be softer (lower compression) at constant COR or 2) have a higher COR at equal compression, or any combination thereof, when compared to a core equivalently prepared without a soft and fast agent. Preferably, the thermoset core layer compositions may contain about 0.05 phr to 10.0 phr soft and fast agent. In one embodiment, the soft and fast agent is present in an amount of about 0.05 phr to 3.0 phr, preferably about 0.05 phr to 2.0 phr, more preferably about 0.05 phr to 1.0 phr. In another embodiment, the soft and fast agent is present in an amount of about 2.0 phr to 5.0 phr, preferably about 2.35 phr to 4.0 phr, and more preferably about 2.35 phr to 3.0 phr. Suitable soft and fast agents include, but are not limited to, organosulfur or metal-containing organosulfur compounds, an organic sulfur compound, including mono, di, and polysulfides, a thiol, or mercapto compound, an inorganic sulfide compound, a Group VIA compound, or mixtures thereof. The soft and fast agent component may also be a blend of an organosulfur compound and an inorganic sulfide compound.

Fillers may be added to the thermoset rubber layer compositions typically include, but are not limited to, processing aids and/or compounds to affect rheological and mixing properties, density-modifying fillers, tear strength, or reinforcement fillers, and the like. Fillers include materials such as tungsten, zinc oxide, barium sulfate, silica, calcium carbonate, zinc carbonate, metals, metal oxides and salts, regrind (recycled core material typically ground to about 30 mesh particle size), high-Mooney-viscosity rubber regrind, trans-rubber regrind (recycled core material containing high trans isomer of polybutadiene), and the like. When trans-regrind is present, the amount of trans isomer is preferably between about 10% and 60%. The fillers are generally inorganic and suitable fillers include numerous metals or metal oxides, such as zinc oxide and tin oxide, as well as barium sulfate, zinc sulfate, calcium carbonate, barium carbonate, clay, tungsten, tungsten carbide, an array of silicas, and mixtures thereof. Fillers may also include various foaming agents or blowing agents which may be readily selected by one of ordinary skill in the art. Fillers may include polymeric, ceramic, metal, and glass microspheres may be solid or hollow, and filled or unfilled. Fillers may be added to one or more layers of the golf ball to modify the density thereof.

The thermoset rubber shell and/or core layers may optionally include at least one additive and/or filler. These materials are also suitable for inclusion in the thermoplastic layers of the present invention. Suitable additives and fillers include, but are not limited to, chemical blowing and foaming agents, optical brighteners, coloring agents, fluorescent agents, whitening agents, UV absorbers, light stabilizers, defoaming agents, processing aids, antioxidants, stabilizers, softening agents, fragrance components, plasticizers, impact modifiers, TiO₂, acid copolymer wax, surfactants, performance additives (e.g., A-C performance additives, particularly A-C low molecular weight ionomers and copolymers, A-C oxidized polyethylenes, and A-C ethylene vinyl acetate waxes, commercially available from Honeywell International Inc.), fatty acid amides (e.g., ethylene bis-stearamide and ethylene bis-oleamide), fatty acids and salts thereof (e.g., stearic acid, oleic acid, zinc stearate, magnesium stearate, zinc oleate, and magnesium oleate), and fillers, such as zinc oxide, tin oxide, barium sulfate, zinc sulfate, calcium oxide, calcium carbonate, zinc carbonate, barium carbonate, tungsten, tungsten carbide, silica, lead silicate, regrind, clay, mica, talc, nano-fillers, carbon black, glass flake, milled glass, flock, fibers, and mixtures thereof. Suitable additives are more fully described in, U.S. Pat. No. 7,041,721 which issued on May 9, 2006, the disclosure of which is hereby incorporated herein by reference. In a particular embodiment, the total amount of additive(s) and filler(s) present in the particle composition is 20 wt % or less, or 15 wt % or less, or 12 wt % or less, or 10 wt % or less, or 9 wt % or less, or 6 wt % or less, or 5 wt % or less, or 4 wt % or less, or 3 wt % or less, or within a range having a lower limit of 0 or 2 or 3 or 5 wt %, based on the total weight of the particle composition, and an upper limit of 9 or 10 or 12 or 15 or 20 wt %, based on the total weight of the particle composition. In a particular aspect of this embodiment, the particle composition includes fillers selected from carbon black, micro- and nano-scale clays and organoclays, including (e.g., CLOISITE and NANOFIL nanoclays, commercially available from Southern Clay Products, Inc.; NANOMAX and NANOMER nanoclays, commercially available from Nanocor, Inc., and PERKALITE nanoclays, commercially available from Akzo Nobel Polymer Chemicals), micro- and nano-scale talcs (e.g., LUZENAC HAR high aspect ratio talcs, commercially available from Luzenac America, Inc.), glass (e.g., glass flake, milled glass, microglass, and glass fibers), micro- and nano-scale mica and mica-based pigments (e.g., IRIODIN pearl luster pigments, commercially available from The Merck Group), and combinations thereof. Particularly suitable combinations of fillers include, but are not limited to, micro-scale fillers combined with nano-scale fillers, and organic fillers with inorganic fillers.

For the thermoset rubber layers of the invention, the fillers and/or additives are present in an amount of about 50 wt % or less, preferably 30 wt % or less, more preferably 20 wt % or less, and most preferably 15 wt % or less, based on the total weight of the composition. Alternatively, for the thermoplastic layers of the invention, the fillers and/or additives are present in an amount of about 10 wt % or less, more preferably 6 wt % or less, and most preferably 3 wt % or less, based on the total weight of the composition.

The particle composition optionally includes one or more melt flow modifiers. Suitable melt flow modifiers include materials which increase the melt flow of the composition, as measured using ASTM D-1238, condition E, at 190° C., using a 2160-g weight. Examples of suitable melt flow modifiers include, but are not limited to, fatty acids and fatty acid salts, including, but not limited to, those disclosed in U.S. Pat. No. 5,306,760, the disclosure of which is hereby incorporated herein by reference; fatty amides and salts thereof; polyhydric alcohols, including, but not limited to, those disclosed in U.S. Pat. Nos. 7,365,128 and 8,163,823, the entire disclosures of which are hereby incorporated herein by reference; polylactic acids, including, but not limited to, those disclosed in U.S. Pat. No. 7,642,319, the disclosure of which is hereby incorporated herein by reference; and the modifiers disclosed in U.S. Pat. No. 8,163,823 and U.S. Patent Application Publication No. 2009/0203469, the disclosures of which are hereby incorporated herein by reference. Flow enhancing additives also include, but are not limited to, montanic acids, esters of montanic acids and salts thereof, bis-stearoylethylenediamine, mono- and polyalcohol esters such as pentaerythritol tetrastearate, zwitterionic compounds, and metallocene-catalyzed polyethylene and polypropylene wax, including maleic anhydride modified versions thereof, amide waxes and alkylene diamides such as bistearamides. Particularly suitable fatty amides include, but are not limited to, saturated fatty acid monoamides (e.g., lauramide, palmitamide, arachidamide behenamide, stearamide, and 12-hydroxy stearamide); unsaturated fatty acid monoamides (e.g., oleamide, erucamide, and ricinoleamide); N-substituted fatty acid amides (e.g., N-stearyl stearamide, N-behenyl behenamide, N-stearyl behenamide, N-behenyl stearamide, N-oleyl oleamide, N-oleyl stearamide, N-stearyl oleamide, N-stearyl erucamide, erucyl erucamide, and erucyl stearamide, N-oleyl palmitamide, methylol amide (more preferably, methylol stearamide, methylol behenamide); saturated fatty acid bis-amides (e.g., methylene bis-stearamide, ethylene bis-stearamide, ethylene bis-isostearamide, ethylene bis-hydroxystearamide, ethylene bis-behenamide, hexamethylene bis-stearamide, hexamethylene bis-behenamide, hexamethylene bis-hydroxystearamide, N,N′-distearyl adipamide, and N,N′-distearyl sebacamide); unsaturated fatty acid bis-amides (e.g., ethylene bis-oleamide, hexamethylene bis-oleamide, N,N′-dioleyl adipamide, N,N′-dioleyl sebacamide); and saturated and unsaturated fatty acid tetra amides, stearyl erucamide, ethylene bis stearamide and ethylene bis oleamide. Suitable examples of commercially available fatty amides include, but are not limited to, KEMAMIDE fatty acids, such as KEMAMIDE B (behenamide/arachidamide), KEMAMIDE W40 (N,N′-ethylenebisstearamide), KEMAMIDE P181 (oleyl palmitamide), KEMAMIDE S (stearamide), KEMAMIDE U (oleamide), KEMAMIDE E (erucamide), KEMAMIDE O (oleamide), KEMAMIDE W45 (N,N′-ethylenebisstearamide), KENAMIDE W20 (N,N′-ethylenebisoleamide), KEMAMIDE E180 (stearyl erucamide), KEMAMIDE E221 (erucyl erucamide), KEMAMIDE S180 (stearyl stearamide), KEMAMIDE 5221 (erucyl stearamide), commercially available from Chemtura Corporation; and CRODAMIDE fatty amides, such as CRODAMIDE OR (oleamide), CRODAMIDE ER (erucamide), CRODAMIDE SR (stereamide), CRODAMIDE BR (behenamide), CRODAMIDE 203 (oleyl palmitamide), and CRODAMIDE 212 (stearyl erucamide), commercially available from Croda Universal Ltd.

The shell layer, and intermediate and outer core layers of the hollow golf ball may also be formed from thermoplastic materials such as ionomeric polymers, and highly- and fully-neutralized ionomers (HNP). Acid moieties of the HNP's, typically ethylene-based ionomers, are preferably neutralized greater than about 80%, more preferably greater than about 90%, and most preferably about 100%. The HNP's can be also be blended with a second polymer component, which, if containing an acid group, may be neutralized in a conventional manner, by the organic fatty acids of the present invention, or both. The second polymer component, which may be partially- or fully-neutralized, preferably comprises ionomeric copolymers and terpolymers, ionomer precursors, thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes, polyureas, thermoplastic elastomers, polybutadiene rubber, balata, metallocene-catalyzed polymers (grafted and non-grafted), single-site polymers, high-crystalline acid polymers, cationic ionomers, and the like. HNP polymers typically have a material hardness of between about 20 and about 80 Shore D, and a flexural modulus of between about 3,000 psi and about 200,000 psi.

Preferably, the HNP's are ionomers and/or their acid precursors that are preferably neutralized, either fully or partially, with organic acid copolymers or the salts thereof. The acid copolymers are preferably α-olefin, such as ethylene, C₃₋₈ α,β-ethylenically unsaturated carboxylic acid, such as acrylic and methacrylic acid, copolymers. They may optionally contain a softening monomer, such as alkyl acrylate and alkyl methacrylate, wherein the alkyl groups have from 1 to 8 carbon atoms.

The acid copolymers can be described as E/X/Y copolymers where E is ethylene, X is an α,β-ethylenically unsaturated carboxylic acid, and Y is a softening comonomer. In a preferred embodiment, X is acrylic or methacrylic acid and Y is a C₁₋₈ alkyl acrylate or methacrylate ester. X is preferably present in an amount from about 1 to about 35 weight percent of the polymer, more preferably from about 5 to about 30 weight percent of the polymer, and most preferably from about 10 to about 20 weight percent of the polymer. Y is preferably present in an amount from about 0 to about 50 weight percent of the polymer, more preferably from about 5 to about 25 weight percent of the polymer, and most preferably from about 10 to about 20 weight percent of the polymer.

Specific acid-containing ethylene copolymers include, but are not limited to, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/n-butyl acrylate, ethylene/methacrylic acid/iso-butyl acrylate, ethylene/acrylic acid/iso-butyl acrylate, ethylene/methacrylic acid/n-butyl methacrylate, ethylene/acrylic acid/methyl methacrylate, ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl methacrylate, and ethylene/acrylic acid/n-butyl methacrylate. Preferred acid-containing ethylene copolymers include, ethylene/methacrylic acid/n-butyl acrylate, ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/acrylic acid/ethyl acrylate, ethylene/methacrylic acid/ethyl acrylate, and ethylene/acrylic acid/methyl acrylate copolymers. The most preferred acid-containing ethylene copolymers are, ethylene/(meth)acrylic acid/n-butyl, acrylate, ethylene/(meth)acrylic acid/ethyl acrylate, and ethylene/(meth)acrylic acid/methyl acrylate copolymers.

Ionomers are typically neutralized with a metal cation, such as Li, Na, Mg, K, Ca, or Zn. It has been found that by adding sufficient organic acid or salt of organic acid, along with a suitable base, to the acid copolymer or ionomer, however, the ionomer can be neutralized, without losing processability, to a level much greater than for a metal cation. Preferably, the acid moieties are neutralized greater than about 80%, preferably from 90-100%, most preferably 100% without losing processability. This accomplished by melt-blending an ethylene α,β-ethylenically unsaturated carboxylic acid copolymer, for example, with an organic acid or a salt of organic acid, and adding a sufficient amount of a cation source to increase the level of neutralization of all the acid moieties (including those in the acid copolymer and in the organic acid) to greater than 90%, (preferably greater than 100%).

The organic acids are typically aliphatic, mono- or multi-functional (saturated, unsaturated, or multi-unsaturated) organic acids. Salts of these organic acids may also be employed. The salts of organic acids of the present invention include the salts of barium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium, strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin, or calcium, salts of fatty acids, particularly stearic, behenic, erucic, oleic, linoelic or dimerized derivatives thereof. It is preferred that the organic acids and salts of the present invention be relatively non-migratory (they do not bloom to the surface of the polymer under ambient temperatures) and non-volatile (they do not volatilize at temperatures required for melt-blending).

The ionomers of the invention may also be more conventional ionomers, i.e., partially-neutralized with metal cations. The acid moiety in the acid copolymer is neutralized about 1 to about 90%, preferably at least about 20 to about 75%, and more preferably at least about 40 to about 70%, to form an ionomer, by a cation such as lithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, or a mixture thereof.

Preferred thermoplastic materials are disclosed in U.S. Pat. No. 7,591,742, the disclosure of which is incorporated herein in its entirety by reference thereto.

Thermoplastic elastomers (TPE) many also be used for the thermoplastic shell or core layers and/or to modify the properties of the shell and/or core layers, or the uncured rubber core layer stock by blending with the base thermoset rubber. These TPEs include natural or synthetic balata, or high trans-polyisoprene, high trans-polybutadiene, or any styrenic block copolymer, such as styrene ethylene butadiene styrene, styrene-isoprene-styrene, etc., a metallocene or other single-site catalyzed polyolefin such as ethylene-octene, or ethylene-butene, or thermoplastic polyurethanes (TPU), including copolymers, e.g. with silicone. Other suitable TPEs for blending with the thermoset rubbers of the present invention include PEBAX®, which is believed to comprise polyether amide copolymers, HYTREL®, which is believed to comprise polyether ester copolymers, thermoplastic urethane, and KRATON®, which is believed to comprise styrenic block copolymers elastomers. Any of the TPEs or TPUs above may also contain functionality suitable for grafting, including maleic acid or maleic anhydride.

Additional polymers may also optionally be incorporated into the base rubber for the shell and core layers. Examples include, but are not limited to, thermoset elastomers such as core regrind, thermoplastic vulcanizate, copolymeric ionomer, terpolymeric ionomer, polycarbonate, polyamide, copolymeric polyamide, polyesters, polyvinyl alcohols, acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate, polyphenylene ether, impact-modified polyphenylene ether, high impact polystyrene, diallyl phthalate polymer, styrene-acrylonitrile polymer (SAN) (including olefin-modified SAN and acrylonitrile-styrene-acrylonitrile polymer), styrene-maleic anhydride copolymer, styrenic copolymer, functionalized styrenic copolymer, functionalized styrenic terpolymer, styrenic terpolymer, cellulose polymer, liquid crystal polymer, ethylene-vinyl acetate copolymers, polyurea, and polysiloxane or any metallocene-catalyzed polymers of these species.

Suitable polyamides for use as an additional polymeric material in compositions within the scope of the present invention also include resins obtained by: (1) polycondensation of (a) a dicarboxylic acid, such as oxalic acid, adipic acid, sebacic acid, terephthalic acid, isophthalic acid, or 1,4-cyclohexanedicarboxylic acid, with (b) a diamine, such as ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, or decamethylenediamine, 1,4-cyclohexanediamine, or m-xylylenediamine; (2) a ring-opening polymerization of cyclic lactam, such as ε-caprolactam or Ω-laurolactam; (3) polycondensation of an aminocarboxylic acid, such as 6-aminocaproic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, or 12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam with a dicarboxylic acid and a diamine. Specific examples of suitable polyamides include NYLON 6, NYLON 66, NYLON 610, NYLON 11, NYLON 12, copolymerized NYLON, NYLON MXD6, and NYLON 46.

The hollow interior of the shell layer has a diameter of about 0.1 inches to about 1.1 inches, preferably about 0.2 inches to about 0.9 inches, more preferably about 0.25 inches to about 0.75 inches, and most preferably about 0.3 inches to about 0.5 inches. In one preferred embodiment, the hollow interior of the shell layer has a diameter of greater than 0.5 inches. The shell layer has a thickness that ranges from 0.01 inches to about 0.4 inches. When the shell layer is desired to be relatively thick, the shell layer thickness is about 0.125 inches to about 0.375 inches, preferably about 0.2 inches to about 0.3125 inches, more preferably about 0.25 inches to about 0.3 inches, and most preferably about 0.26 inches to about 0.275 inches. When the shell layer is desired to be relatively thin, the shell layer thickness is about 0.01 inches to about 0.1 inches, preferably about 0.02 inches to about 0.075 inches, more preferably about 0.025 inches to about 0.04 inches, and most preferably about 0.03 inches to about 0.035 inches. When the shell layer is relatively thin and formed from a thermoplastic material, the TP material is preferably selected to be somewhat heat resistant (or blended with a heat resistant TP material) to avoid melting of the layer by subsequent molding of additional core and/or cover layers.

With the dimensions of the hollow interior in mind, the hollow cores (shell layer, shell layer and outer core layer(s)) of the invention preferably have an outer diameter of about 0.75 inches to about 1.58 inches, preferably about 1.0 inches to about 1.57 inches, more preferably about 1.3 inches to about 1.56 inches, and most preferably about 1.4 inches to about 1.55 inches. In preferred embodiments, the shell layer has an outer diameter of about 0.75 inches, 1.0 inches, 1.20 inches, or 1.30 inches, with a most preferred outer diameter being 0.75 inches or 1.0 inches. In an alternative embodiment, the outer core layer should have an outer diameter (the entire hollow core, shell layer plus outer core layer) of about 1.30 inches to about 1.62 inches, preferably 1.4 inches to about 1.6 inches, and more preferably about 1.5 inches to about 1.59 inches. In preferred embodiments, the outer core layer has an outer diameter of about 1.51 inches, 1.53 inches, or most preferably 1.550 inches.

The inner and outer cover layers preferably have a thickness of about 0.010 to 0.080 inches, more preferably about 0.015 to 0.060 inches, and most preferably about 0.020 to 0.040 inches. Alternatively, the inner and outer cover layers have a thickness of about 0.015 inches to about 0.055 inches, more preferably about 0.02 inches to about 0.04 inches, and most preferably about 0.025 inches to about 0.035 inches. The inner cover layer, if present, preferably has a hardness of about 60 Shore D or greater, more preferably about 65 Shore D or greater, and most preferably about 70 Shore D or greater. The inner cover layer is preferably harder than the outer cover layer although in one embodiment the outer cover layer is harder than the inner cover layer. The outer cover layer preferably has a hardness of about 60 Shore D or less, more preferably about 55 Shore D or less, and most preferably about 50 Shore D or less.

Formation of the shell and outer core layers of the invention may be accomplished in a variety of ways, such as those disclosed in U.S. Pat. Nos. 5,480,155; 6,315,683, and 8,262,508, the disclosures of which are incorporated herein, in their entirety, by reference thereto.

In a preferred embodiment, the golf ball of the present invention includes a hollow core. The hollow core is formed from spherical inner core shell layer that contains a spherical hollow portion in its interior. The shell layer is formed from a thermoset rubber composition and has an outer surface, an inner surface, and an inner diameter to define the dimensions of the hollow center. In this embodiment, a single outer core layer is formed around the shell layer to create a hollow golf ball core. The outer core layer is also formed from a thermoset material, which may be the same rubber composition as the shell layer but is preferably a different thermoset rubber composition. A single cover layer or multiple cover layers are formed over the TS/TS hollow core. Preferably, an inner cover layer and an outer cover layer are formed over the outer core layer. In one embodiment, the inner cover includes an ionomeric material and the outer cover layer includes a polyurea or, preferably, a polyurethane. The outer cover layer is typically softer than the inner cover layer, such as where the inner cover has a hardness of greater than about 60 Shore D and the outer cover layer has a hardness of less than about 60 Shore D.

In the above embodiment, the hollow center preferably has a diameter of about 0.51 to 1.1 inches. The surface hardness of the shell layer is preferably greater than the hardness of the inner surface of the shell layer by about 3 to 25 Shore C to define a first hardness gradient. In a preferred embodiment, the thermoset outer core layer has a hardness gradient that is different from the hardness gradient of the thermoset shell layer. Most preferably, the shell layer has a surface hardness greater than about 55 Shore C.

The thermoset inner core shell layer has a coefficient of restitution (COR) less than about 0.750 when measured at an incoming velocity of 125 ft/s. Preferably, the COR is less than about 0.700, more preferably about 0.500 to 0.700, and most preferably about 0.600 to 0.700. The overall hollow core (the combination of the thermoset shell layer and the thermoset outer core layer) has a COR, measured at an incoming velocity of 125 ft/s, higher than the COR of the inner core shell layer by greater than about 5%, more preferably about 10 to 50%, and most preferably about 15 to 30%.

In an alternative embodiment, the hardness gradient of the thermoset outer core layer has a ‘zero hardness gradient’. The zero hardness gradient is typically about 0 Shore C (defined herein as ±2 Shore C). The hardness gradient of the thermoset outer core layer may also have a ‘negative hardness gradient’, preferably about 3 to 25 Shore C, more preferably about 5 to 20 Shore C, and most preferably about 8 to 15 Shore C. The hardness gradient of the thermoset outer core layer may also have a ‘positive hardness gradient’, preferably about 3 to 25 Shore C, more preferably about 5 to 20 Shore C, and most preferably about 8 to 15 Shore C.

The golf ball has a first volume and the hollow center has a second volume. The volume of the hollow center is about 2% to 30% of the golf ball volume, more preferably about 5% to 25% of the golf ball volume, and most preferably about 10% to 20% of the golf ball volume.

In another embodiment of the invention, the hollow core further includes a thermoplastic intermediate core layer disposed between the thermoset shell layer and the thermoset outer core layer. In still another embodiment, the hollow core further includes a thermoset intermediate core layer disposed between the thermoset shell layer and the thermoset outer core layer. The intermediate core layer may formed from a thermoset rubber composition which is the same or different from the thermoset rubber compositions used to form the thermoset shell layer or the thermoset outer core layer. In these embodiments, the hollow center preferably has a diameter of about 0.15 to 1.1 inches, the shell layer has a surface hardness greater than an inner surface hardness by about 10 to 25 Shore C to define a hardness gradient, preferably a ‘positive hardness gradient’. The thermoset outer core layer preferably has a hardness gradient that is different from the hardness gradient of the shell layer or the intermediate layer.

The hollow core of the present invention is covered by at least one cover layer. An intermediate layer, such as an inner cover layer, may optionally be disposed about the hollow core, with the cover layer formed around the intermediate layer as an outer cover layer. While any of the thermoplastic materials disclosed herein may be suitable for the inner or outer cover layers of the invention, in a preferred embodiment the outermost cover is formed from a castable polyurea or a castable polyurethane; castable hybrid poly(urethane/urea); and castable hybrid poly(urea/urethane). Suitable polyurethanes include those disclosed in U.S. Pat. Nos. 5,334,673 and 6,506,851. Suitable polyureas include those disclosed in U.S. Pat. Nos. 5,484,870 and 6,835,794. These patents are incorporated herein by reference thereto.

Other suitable polyurethane compositions comprise a reaction product of at least one polyisocyanate and at least one curing agent. The curing agent can include, for example, one or more polyamines, one or more polyols, or a combination thereof. The polyisocyanate can be combined with one or more polyols to form a prepolymer, which is then combined with the at least one curing agent. Thus, the polyols described herein are suitable for use in one or both components of the polyurethane material, i.e., as part of a prepolymer and in the curing agent. More suitable polyurethanes are described in U.S. Pat. No. 7,331,878, which is incorporated by reference in its entirety.

Any polyisocyanate available to one of ordinary skill in the art is suitable for use according to the invention. Exemplary polyisocyanates include, but are not limited to, 4,4′-diphenylmethane diisocyanate (MDI); polymeric MDI; carbodiimide-modified liquid MDI; 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI); p-phenylene diisocyanate (PPDI); m-phenylene diisocyanate (MPDI); toluene diisocyanate (TDI); 3,3′-dimethyl-4,4′-biphenylene diisocyanate; isophoronediisocyanate; 1,6-hexamethylene diisocyanate (HDI); naphthalene diisocyanate; xylene diisocyanate; p-tetramethylxylene diisocyanate; m-tetramethylxylene diisocyanate; ethylene diisocyanate; propylene-1,2-diisocyanate; tetramethylene-1,4-diisocyanate; cyclohexyl diisocyanate; dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate; cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate; 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; methyl cyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of 2,4,4-trimethyl-1,6-hexane diisocyanate; tetracene diisocyanate; napthalene diisocyanate; anthracene diisocyanate; isocyanurate of toluene diisocyanate; uretdione of hexamethylene diisocyanate; and mixtures thereof. Polyisocyanates are known to those of ordinary skill in the art as having more than one isocyanate group, e.g., di-isocyanate, triisocyanate, and tetra-isocyanate. Preferably, the polyisocyanate includes MDI, PPDI, TDI, or a mixture thereof, and more preferably, the polyisocyanate includes MDI. It should be understood that, as used herein, the term MDI includes 4,4′-diphenylmethane diisocyanate, polymeric MDI, carbodiimide-modified liquid MDI, and mixtures thereof and, additionally, that the diisocyanate employed may be “low free monomer,” understood by one of ordinary skill in the art to have lower levels of “free” monomer isocyanate groups, typically less than about 0.1% free monomer isocyanate groups. Examples of “low free monomer” diisocyanates include, but are not limited to Low Free Monomer MDI, Low Free Monomer TDI, and Low Free Monomer PPDI.

The at least one polyisocyanate should have less than about 14% unreacted NCO groups. Preferably, the at least one polyisocyanate has no greater than about 8.0% NCO, more preferably no greater than about 7.8%, and most preferably no greater than about 7.5% NCO with a level of NCO of about 7.2 or 7.0, or 6.5% NCO commonly used.

Any polyol available to one of ordinary skill in the art is suitable for use according to the invention. Exemplary polyols include, but are not limited to, polyether polyols, hydroxy-terminated polybutadiene (including partially/fully hydrogenated derivatives), polyester polyols, polycaprolactone polyols, and polycarbonate polyols. In one preferred embodiment, the polyol includes polyether polyol. Examples include, but are not limited to, polytetramethylene ether glycol (PTMEG), polyethylene propylene glycol, polyoxypropylene glycol, and mixtures thereof. The hydrocarbon chain can have saturated or unsaturated bonds and substituted or unsubstituted aromatic and cyclic groups. Preferably, the polyol of the present invention includes PTMEG.

In another embodiment, polyester polyols are included in the polyurethane material. Suitable polyester polyols include, but are not limited to, polyethylene adipate glycol; polybutylene adipate glycol; polyethylene propylene adipate glycol; o-phthalate-1,6-hexanediol; poly(hexamethylene adipate)glycol; and mixtures thereof. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups.

In another embodiment, polycaprolactone polyols are included in the materials of the invention. Suitable polycaprolactone polyols include, but are not limited to, 1,6-hexanediol-initiated polycaprolactone, diethylene glycol initiated polycaprolactone, trimethylol propane initiated polycaprolactone, neopentyl glycol initiated polycaprolactone, 1,4-butanediol-initiated polycaprolactone, and mixtures thereof. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups.

In yet another embodiment, polycarbonate polyols are included in the polyurethane material of the invention. Suitable polycarbonates include, but are not limited to, polyphthalate carbonate and poly(hexamethylene carbonate)glycol. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups. In one embodiment, the molecular weight of the polyol is from about 200 to about 4000.

Polyamine curatives are also suitable for use in the polyurethane composition of the invention and have been found to improve cut, shear, and impact resistance of the resultant balls. Preferred polyamine curatives include, but are not limited to, 3,5-dimethylthio-2,4-toluenediamine and isomers thereof; 3,5-diethyltoluene-2,4-diamine and isomers thereof, such as 3,5-diethyltoluene-2,6-diamine; 4,4′-bis-(sec-butylamino)-diphenylmethane; 1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline); 4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyldiamino diphenyl methane; p,p′-methylene dianiline; m-phenylenediamine; 4,4′-methylene-bis-(2-chloroaniline); 4,4′-methylene-bis-(2,6-diethylaniline); 4,4′-methylene-bis-(2,3-dichloroaniline); 4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane; 2,2′,3,3′-tetrachloro diamino diphenylmethane; trimethylene glycol di-p-aminobenzoate; and mixtures thereof. Preferably, the curing agent of the present invention includes 3,5-dimethylthio-2,4-toluenediamine and isomers thereof, such as ETHACURE® 300, commercially available from Albermarle Corporation of Baton Rouge, La. Suitable polyamine curatives, which include both primary and secondary amines, preferably have molecular weights ranging from about 64 to about 2000.

At least one of a diol, triol, tetraol, or hydroxy-terminated curatives may be added to the aforementioned polyurethane composition. Suitable diol, triol, and tetraol groups include ethylene glycol; diethylene glycol; polyethylene glycol; propylene glycol; polypropylene glycol; lower molecular weight polytetramethylene ether glycol; 1,3-bis(2-hydroxyethoxy)benzene; 1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene; 1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene; 1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(β-hydroxyethyl) ether; hydroquinone-di-(β-hydroxyethyl) ether; and mixtures thereof. Preferred hydroxy-terminated curatives include 1,3-bis(2-hydroxyethoxy)benzene; 1,3-bis-[2-(2-hydroxyethoxy) ethoxy]benzene; 1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene; 1,4-butanediol, and mixtures thereof. Preferably, the hydroxy-terminated curatives have molecular weights ranging from about 48 to 2000. It should be understood that molecular weight, as used herein, is the absolute weight average molecular weight and would be understood as such by one of ordinary skill in the art.

Both the hydroxy-terminated and amine curatives can include one or more saturated, unsaturated, aromatic, and cyclic groups. Additionally, the hydroxy-terminated and amine curatives can include one or more halogen groups. The polyurethane composition can be formed with a blend or mixture of curing agents. If desired, however, the polyurethane composition may be formed with a single curing agent.

In a preferred embodiment of the present invention, saturated polyurethanes are used to form one or more of the cover layers, preferably the outer cover layer, and may be selected from both castable thermoset and thermoplastic polyurethanes. In this embodiment, the saturated polyurethanes of the present invention are substantially free of aromatic groups or moieties. Saturated polyurethanes suitable for use in the invention are a product of a reaction between at least one polyurethane prepolymer and at least one saturated curing agent. The polyurethane prepolymer is a product formed by a reaction between at least one saturated polyol and at least one saturated diisocyanate. As is well known in the art, that a catalyst may be employed to promote the reaction between the curing agent and the isocyanate and polyol, or the curing agent and the prepolymer.

Additionally, polyurethane can be replaced with or blended with a polyurea material. Polyureas are distinctly different from polyurethane compositions. The polyurea-based compositions are preferably saturated in nature. The polyurea compositions may be formed from the reaction product of an isocyanate and polyamine prepolymer crosslinked with a curing agent. For example, polyurea-based compositions of the invention may be prepared from at least one isocyanate, at least one polyether amine, and at least one diol curing agent or at least one diamine curing agent.

While any of the embodiments herein may have any known dimple number and pattern, a preferred number of dimples is 252 to 456, and more preferably is 330 to 392. The dimples may comprise any width, depth, and edge angle disclosed in the prior art and the patterns may comprises multitudes of dimples having different widths, depths and edge angles. The parting line configuration of said pattern may be either a straight line or a staggered wave parting line (SWPL). Most preferably the dimple number is 330, 332, or 392 and comprises 5 to 7 dimples sizes and the parting line is a SWPL.

In any of these embodiments the single-layer core may be replaced with a 2 or more layer core wherein at least one core layer has a negative hardness gradient. Other than in the operating examples, or unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages such as those for amounts of materials and others in the specification may be read as if prefaced by the word “about” even though the term “about” may not expressly appear with the value, amount or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Furthermore, when numerical ranges of varying scope are set forth herein, it is contemplated that any combination of these values inclusive of the recited values may be used.

While it is apparent that the illustrative embodiments of the invention disclosed herein fulfill the objective stated above, it is appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments, which would come within the spirit and scope of the present invention. 

What is claimed is:
 1. A golf ball comprising a hollow core, the golf ball comprising: a spherical inner core shell layer comprising a first thermoset rubber composition, the shell layer having an outer surface, an inner surface, and an inner diameter to define a hollow center; an outer core layer disposed about the shell layer, the outer core layer comprising a second thermoset material; an inner cover layer disposed about the outer core layer, the inner cover comprising an ionomeric material and having a first hardness; and an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a second hardness less than the first; wherein the hollow center has a diameter of about 0.51 to 1.1 inches, the shell layer has a surface hardness greater than an inner surface hardness by about 3 to 25 Shore C to define a first hardness gradient, and the outer core layer has a second hardness gradient different from the first.
 2. The golf ball of claim 1, wherein the shell layer has a surface hardness greater than about 55 Shore C.
 3. The golf ball of claim 1, wherein the spherical inner core shell layer has a coefficient of restitution less than about 0.700 when measured at an incoming velocity of 125 ft/s.
 4. The golf ball of claim 1, wherein the outer core layer has a coefficient of restitution, measured at an incoming velocity of 125 ft/s, higher than the coefficient of restitution, measured at an incoming velocity of 125 ft/s, of the inner core shell layer by 10-50%.
 5. The golf ball of claim 1, wherein the second hardness gradient is about 0 Shore C.
 6. The golf ball of claim 1, wherein the second hardness gradient is a negative hardness gradient of about 2 to 25 Shore C.
 7. The golf ball of claim 1, wherein the second hardness gradient is a positive hardness gradient of about 3 to 10 Shore C.
 8. The golf ball of claim 1, wherein the inner cover has a hardness of greater than about 60 Shore D and the outer cover layer has a hardness of less than about 60 Shore D.
 9. The golf ball of claim 1, wherein the golf ball has a first volume and the hollow center has a second volume that is about 2% to 30% of the first volume.
 10. A golf ball comprising a hollow core, the golf ball comprising: a spherical inner core shell layer formed from a first thermoset rubber composition, the shell layer having an outer surface, an inner surface, and an inner diameter to define a hollow center; an outer core layer comprising a second thermoset material; a thermoplastic intermediate core layer disposed between the shell layer and the outer core layer; an inner cover layer disposed about the outer core layer, the inner cover comprising an ionomeric material and having a material hardness greater than about 60 Shore D; and an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a material hardness of less than about 60 Shore D; wherein the hollow center has a diameter of about 0.15 to 1.1 inches, the shell layer has a surface hardness greater than an inner surface hardness by about 10 to 25 Shore C to define a first hardness gradient, and the thermoset outer core layer has a second hardness gradient different from the first.
 11. The golf ball of claim 10, wherein the second hardness gradient is about 0 Shore C.
 12. The golf ball of claim 10, wherein the second hardness gradient is a negative hardness gradient of about 2 to 25 Shore C.
 13. The golf ball of claim 10, wherein the second hardness gradient is a positive hardness gradient of about 3 to 10 Shore C.
 14. A golf ball comprising a hollow core, the golf ball comprising: a spherical inner core shell layer formed from a first thermoset rubber composition, the shell layer having an outer surface, an inner surface, and an inner diameter to define a hollow center; an outer core layer comprising a second thermoset material; a thermoset intermediate core layer disposed between the shell layer and the outer core layer, the intermediate core layer comprising a third thermoset rubber composition different from the first and the second; an inner cover layer disposed about the outer core layer, the inner cover comprising an ionomeric material and having a first hardness; and an outer cover layer disposed about the inner cover layer, the outer cover comprising a polyurea or a polyurethane and having a second hardness less than the first; wherein the hollow center has a diameter of about 0.15 to 1.1 inches, the shell layer has a surface hardness greater than an inner surface hardness by about 10 to 25 Shore C to define a first hardness gradient, and at least one of the thermoset outer core layer or thermoset intermediate core layer has a hardness gradient different from the first.
 15. The golf ball of claim 14, wherein the second hardness gradient is about 0 Shore C.
 16. The golf ball of claim 14, wherein the second hardness gradient is a negative hardness gradient of about 2 to 25 Shore C.
 17. The golf ball of claim 14, wherein the second hardness gradient is a positive hardness gradient of about 3 to 10 Shore C. 